[WordPress] 添付画像表示ページのタイトルを親投稿のタイトルに合わせる。

wp-my_attachment_title.php

<?php
function my_attachment_title($title, $id) {
  if ( is_admin() )
    return $title;

  $post = is_object($id)
      ? $id
      : $post = get_post($id);

  if ( !$post || $post->post_type !== 'attachment' )
      return $title;

  if ( $post_parent = get_post($post->post_parent) ) {
      $title = intval($post->menu_order) > 0
          ? $post_parent->post_title . ' (' . intval($post->menu_order) . ')'
          : $post_parent->post_title;
      $title = apply_filters('the_title', $title, $post_parent->ID);  	
  }
  unset($post);
  unset($post_parent);

  return $title;
}
add_filter('the_title', 'my_attachment_title', 10, 2);
add_filter('single_post_title', 'my_attachment_title', 10, 2);